It's no secret that Muscle Car performance was on the decline after 1970 or so, but Pontiac engineers pressed on when they created the Super Duty Trans Am package, which was still a screamer in 1974.    The SD-455 was a remarkable engine, a legit race-bred machine among the plummeting compression ratios and horsepower levels of other V8s of the day.  This is a great example of a low-mile and correct 1974 SD-455 Trans Am from the Brothers Collection.